The present invention relates to a common voltage generation circuit, a power supply circuit, a display driver, and a common voltage generation method.
As a liquid crystal panel (electro-optical device) used in an electronic instrument, a simple matrix type liquid crystal panel and an active matrix type liquid crystal panel using a switch element such as a thin film transistor (hereinafter abbreviated as “TFT”) have been known.
The simple matrix type liquid crystal panel can easily reduce power consumption in comparison with the active matrix type liquid crystal panel. However, it is difficult to increase the number of colors and to present a video display by using the simple matrix type liquid crystal panel. The active matrix type liquid crystal panel is suitable for an increase the number of colors and a video display. However, it is difficult to reduce power consumption using the active matrix type liquid crystal panel.
In recent years, a demand for an increase in the number of colors and a video display has been increased for a portable electronic instrument such as a portable telephone in order to provide a high-quality image. Therefore, the active matrix type liquid crystal panel has been increasingly used instead of the simple matrix type liquid crystal panel.
In the active matrix type liquid crystal panel used in a portable electronic instrument, the voltage applied to a liquid crystal element sealed between a pixel electrode and a common electrode which faces the pixel electrode is reversed in scan period units in order to deal with a demand for a liquid crystal AC drive and a low power supply voltage, for example.
In the case of generating a common voltage applied to the common electrode, a high-potential-side voltage and a low-potential-side voltage of the common voltage may be generated by using operational amplifiers. However, it is necessary to provide a power supply voltage to the operational amplifiers using a dual power supply method in order to sufficiently secure the output amplitude of the operational amplifiers. Therefore, since power consumption is increased due to an increase in the power supply voltage of the operational amplifiers, it is difficult to further reduce power consumption.